1. Field of the Invention
The present invention relates to a method and apparatus for accumulative vector drawing, and more particularly, to a method and apparatus for accumulative vector drawing, by which graphics commands are accumulated and rendered in reverse order and during the reverse order rendering, a part of a lower drawing command overlapping with an upper drawing command is not rendered, thereby increasing the speed of executing a drawing command.
2. Description of the Related Art
In a structure such as a windows system in which a picture is drawn by accumulating various figures, a graphics system displays a window, in which figures having a quadrangular shape or other diverse shapes overlap with one another, and iteratively draws an overlapping area between the figures whenever each figure is drawn.
FIG. 1 is a diagram of a conventional display system.
To output a graphics command to a display apparatus, the display system includes a graphics system unit 110, a video unit 120, and a display unit 130, as shown in FIG. 1. A user draws a figure on the display unit 130 using a graphics command interface 111 included in the graphics system unit 110. In addition, the user can set graphics attributes, e.g., color and line thickness, applied to the figure. A data structure that stores the values of these graphics attributes is referred to as a graphics context. The graphics system unit 110 includes a graphics context section 112 managing at least one graphics context. The graphics system unit 110 and the video unit 120 can exchange data with each other directly or by mapping a main memory or the like. A graphics processor 121 included in the video unit 120 converts data received from the graphics system unit 110 and moves the data to a video memory 122. As a result, a graphics command input by the user is stored in the video memory 122 in the form of byte stream information and is transmitted to and displayed on the display unit 130.
FIG. 2 is a flowchart of the fundamental operations of the conventional display system shown in FIG. 1.
Specifically, FIG. 2 illustrates the operations of the graphics system unit 110 included in the conventional display system. Graphics commands are largely divided into drawing commands and attribute setting commands. The graphics system unit 110 determines whether an input graphics command is a drawing command in operation S210. If it is determined that it is a drawing command, the graphics system unit 110 converts drawing vector information into pixel-based scalar information and outputs the pixel-based scalar information to the video unit 120 by storing it in the video memory 122 in operation S220. Meanwhile, if the graphics command is an attribute setting command, the graphics system unit 110 sets an attribute value in the graphics context section 112 in operation S230.
When the conventional technology illustrated in FIGS. 1 and 2 is used in a structure such as a windows system in which a picture is drawn by accumulating figures, an area of a figure that is superimposed on by another figure drawn later and is thus not shown is unnecessarily drawn. When drawing vector information input through the graphics command interface 111 to draw a figure is converted into pixel-based scalar information, all pixels in the figure must be calculated, and such rendering process takes most of the operating time of the graphics system unit 110. In addition, drawing a figure over another figure may cause flickering.
Inventions for solving these problems are disclosed in many patents. For example, U.S. Pat. No. 4,907,174 discloses a method of clipping an overlapping area between windows by using a Z-buffer algorithm in a graphics system having multiple windows.
However, since these inventions do not provide a function that eliminates unnecessary drawing or require complex calculations and expensive hardware, these are not satisfactory enough to solve the problem of delay in executing a graphics command.